allow to run multiple services of a same image

This is a follow-up of #344 (closed) where potential solution was proposed to allow naming of services like

services:
  - image: "postgres:9.5"
    name: "database-one"
  - image: "postgres:9.5"
    name: "database-two"

Some CI workflows requires to use multiple instances of a same service, like migration scripts. My desired use case is to run same version of a service but multiple times, to emulate a cluster of machines on which my application depends on.